In a typical gas-phase propane fuel delivery system, gas under high pressure (up to 220 psi) is fed to a regulator which reduces the pressure to a level compatible with the carburetor of an internal combustion engine. Since the tank pressure is constant, the engine need not be running in order to have gas flow. A solenoid valve may be connected to the output of the regulator to interrupt a gas flow from the regulator in the event of engine shut off. Upon cranking at start up of the internal combustion engine a vacuum switch may be activated by the resulting engine manifold vacuum. The vacuum switch in turn activates the solenoid valve, enabling gas flow from the regulator. The gas flow remains enabled as long as there is sufficient engine vacuum to keep the solenoid valve open, i.e. so long as the engine remains running.
In cold climates, engine starting problems frequently develop. The regulator requires a certain minimum input pressure in order to function properly. However, as the gas tank temperature drops, the vapor pressure internally drops. That reduction in vapor pressure proceeds according to the laws of physics, which state that a confined gas under pressure has a specific vapor pressure at a specific temperature, or, conversely, that a specific gas temperature occurs at a specific gas vapor pressure. If the temperature of the tank gets low enough, the pressure to the regulator may get so low that the propane never transfers to a vapor phase. If this happens, the regulator "freezes", i.e. the regulator pumps liquid into the carburetor. That causes a flooded condition in the carburetor and the engine will not run.
Existing systems address the cold weather limitations of propane fuel systems from various perspectives. However, none of those systems appear to provide a reliable solution that is independent of operator intervention after initial setup. For example, in diesel engines, it has been known to remedy cold weather problems by providing a direct injection of ether into the carburetor to get the engine started, and then to provide further sporadic injections of ether into the carburetor until enough heat has been generated to vaporize the diesel fuel.
Another technique for avoiding regulator freezing is to heat the propane tank, either by gas burners or by some other means, until the desired temperature and pressure conditions are obtained within the tank. Typically, if the unit being run is a generator set, a small enclosure may be formed about the generator set, housing a system for heating the generator set to provide sufficient pressure in the propane tank to cause the regulator output to be in a vapor phase. The space, cost and safety penalties attendant to building such an enclosure, and providing a system for heating the generator set may be entirely unacceptable, particularly when the system is designed for use in remote locations where simple, safe and reliable operation is a high priority.
In practice, the cold weather limitations of contemporary propane fuel systems have frequently required that propane powered equipment be maintained in heated areas and started prior to leaving the heated area. Though this practice avoids persistent problems in starting a propane fuel system that has been left in the ambient air, such practices are directed more towards avoiding problems and limitations of contemporary systems rather than solving those problems.
The present invention is intended to solve these and other problems of conventional propane fuel delivery systems by providing a reliable and economical system that need not be maintained in a heated area, does not require any manual intervention, and does not require heating of the propane tank to effect delivery of vapor-phase propane to the carburetor regulator.